Method and apparatus for monitoring payload

Abstract

In many applications, it is important to measure and display payload weight for a loader vehicle. The subject apparatus and method senses only the hydraulic pressure of a lift cylinder. The payload weight is computed by curve fitting the sensed cylinder pressure to a second order time dependent polynomial and comparing the time dependent polynomial to one of a series of predetermined second order geometric polynomials. The weight computation algorithms used in the payload monitor are applicable to a number of work vehicles having at least one work implement linkage and at least one hydraulic cylinder for modifying the linkage geometry.

We claim: 
     
       1. A method for dynamically measuring and indicating payload weight for a vehicle having at least one lift cylinder for elevating a payload carrier, said vehicle generally executing a work cycle including lifting said payload carrier, said method comprising the steps of: sensing hydraulic pressure in said lift cylinder during said work cycle;   delivering a plurality of signals in response to said sensed pressure:   deriving a second order time dependent polynomial representation of said plurality of signals;   comparing said time dependent polynomial to at least one of a plurality of second order geometric polynomial representations of known payload weights; and   calculating an actual payload weight in response to said comparison.   
     
     
       2. A method, as set forth in claim 1, wherein said time dependent polynomial deriving step includes using an error minimizing technique to fit a predetermined number of said signals to a second order equation. 
     
     
       3. A method, as set forth in claim 1, wherein said lift cylinder extends to elevate said payload carrier, and said geometric polynomial represents a relationship between said sensed pressure and said extension of said lift cylinder. 
     
     
       4. A method, as set forth in claim 3, wherein said comparing step includes comparing ratios of a rate of change in said sensed pressure with respect to time and a rate of change in said lift cylinder extension with respect to time. 
     
     
       5. A method, as set forth in claim 1, wherein said lift cylinder pressure sensing step is performed only during the payload lifting portion of said work cycle. 
     
     
       6. A method, as set forth in claim 1, wherein the vehicle includes a memory device storing said plurality of geometric polynomial representations. 
     
     
       7. A method, as set forth in claim 6, wherein said plurality of geometric polynomial representations are empirically determined. 
     
     
       8. An apparatus for dynamically measuring and indicating payload weight for a vehicle having at least one lift cylinder for elevating a payload carrier, said vehicle generally executing a work cycle including lifting said payload carrier, comprising: means for sensing said lift cylinder hydraulic pressure during said work cycle;   means for delivering a plurality of signals in response to said sensed pressure;   means for deriving a second order time dependent polynomial representation of said plurality of signals;   means for comparing said time dependent polynomial to at least one of a plurality of second order geometric polynomial representations of known payload weights; and   means for calculating an actual payload weight in response to said comparison.   
     
     
       9. An apparatus, as set forth in claim 8, wherein said time dependent polynomial deriving means includes using an error minimizing technique to fit a predetermined number of said signals to a second order equation. 
     
     
       10. An apparatus, as set forth in claim 8, wherein said lift cylinder extends to elevate said payload carrier, and said plurality of geometric polynomials represent a relationship between said sensed pressure and said lift cylinder extension. 
     
     
       11. An apparatus, as set forth in claim 10, wherein said comparing means compares ratios of a rate of change in said sensed pressure with respect to time and a rate of change in said lift cylinder displacement with respect to time. 
     
     
       12. An apparatus, as set forth in claim 8, wherein said means for delivering a plurality of signals delivers said signals only during the payload lifting portion of said work cycle. 
     
     
       13. An apparatus, as set forth in claim 8, including a memory device for storing said plurality of geometric polynomial representations. 
     
     
       14. An apparatus, as set forth in claim 13, wherein said plurality of geometric polynomial representations are empirically determined.